Before his show trial in Hungary in 1948, Robert Vogeler spent three months in a cell sleeping on a board that hovered just above two inches of water. Day and night a bright light bathed his cell, and even then someone would bang on the wall next door just to make sure he couldn't get any sleep. "It is just a question of time before you confess," he said afterwards. "With some it takes a little longer than others, but nobody can resist that treatment indefinitely."

And so Vogeler, who was arrested for spying, buckled under the pressure and played his role in the gruesome farce of Stalin's postwar purges in eastern Europe. "To judge from the way our scripts were written," wrote Vogeler shortly after his forced confession, "it was more important to establish our allegorical identities than to establish our 'guilt'. Each of us in his testimony was obliged to 'unmask' himself for the benefit of the [Soviet-led] press and radio."

A similar script, it has long been clear, has been written at Guantánamo Bay, although this time the lines were for the prosecution rather than the defence. The point of these detentions has never been to see justice done, but rather to provide a teachable moment about the lengths and depths the American state would go to pursue its perceived interests in the war on terror. It was to find a place in which America could operate above and beyond not only international law but its own - a display of unfettered power not merely indifferent to, but openly contemptuous of, global and local norms.

It is a brutal allegory in which Guantánamo is not the exception but the rule: a grotesque exemplar of the Bush administration's reflexive and opportunistic response to the terrorist attacks of 9/11, from the bombing of Iraq to the phone-tapping of its own citizens. Like Abu Ghraib and the "black sites" of rendition, the violations that have taken place there are systemic and systematic. Like the broader war on terror, they have been characterised by criminality and ineptitude. The camp has not hosted a single trial, and only 19 of the remaining 270 detainees have been charged.

"To protest in the name of morality against 'excesses' or 'abuses' is an error that hints at active complicity," wrote Simone de Beauvoir, referring to French atrocities in Algeria. "There are no 'abuses' or 'excesses' here, simply an all-pervasive system."

Detain, bomb, invade, torture and spy now - ask questions later. Such have been the impulses of the Bush years. But "now" inherits a past and bequeaths a legacy. "Later" keeps arriving with answers for which a largely quiescent if not compliant American public appears to have little stomach. A power grab for the state; a black hole for legality; a free rein for the military; a vacuum for democracy. Such have been the hallmarks of the Bush years.

And like so much else in these twilight months of this administration, the warped logic that underpins Guantánamo is unravelling at great pace. The recent supreme court ruling that inmates have the same rights to habeas corpus protection as "enemy combatants" held on US soil has shed its final fig leaf. Meanwhile, last week's congressional testimony and the dissenting voices of some of the inmate's military lawyers bear witness to how low the administration has stooped and how high the decision-making has gone. "The laws and constitution are designed to survive, and remain in force, in extraordinary times," Justice Anthony Kennedy wrote for the supreme court majority. Maybe so. But political cultures are not. They are feathers for every wind that blows, vulnerable to demagogue and democrat alike.

"To hold that the political branches may switch the constitution on or off at will would lead to a regime in which they, not this court, 'say what the law is'," Kennedy continued. But that is precisely what has been happening these past seven years.

Documents released by congressional investigators last week show interrogators have not so much pushed the envelope, as shredded and torched it. Mark Fallon, the deputy commander of the defence department's criminal investigation taskforce, warned Pentagon colleagues in an email in October 2002 that the interrogation techniques they were discussing, and later implemented, would "shock the conscience of any legal body". "This looks like the kind of stuff congressional hearings are made of," he said. "Someone needs to be considering how history will look back at this."

In the same month Jonathan Friedman, a CIA counter-terrorism lawyer, told military and intelligence officials that "torture is basically subject to perception". "If the detainee dies," continued Friedman, "you're doing it wrong."

Throughout, innocence, guilt, facts and evidence have been little more than technicalities. Indeed, the enterprise has been a huge faith-based initiative - guided by the notion that if you believe you are doing the right thing, it doesn't matter what you actually do.

Colonel Morris Davis, the former chief prosecutor for Guantánamo's military commissions, recalled a meeting he had with Pentagon general counsel William Haynes, who oversees Guantánamo's tribunal process, about the forthcoming trials of the detainees. "[Haynes] said these trials will be the Nuremberg of our time," said Davis. Davis then pointed out that the handful of acquittals at Nuremberg had given the proceedings a sense of legitimacy and credibility that across-the-board convictions never would have.

'I said to him that if we come up short and there are some acquittals in our cases, it will at least validate the process," Davis told the Nation. "At which point, [Haynes's] eyes got wide and he said, 'Wait a minute, we can't have acquittals. If we've been holding these guys for so long, how can we explain letting them get off? We can't have acquittals. We've got to have convictions.'"

Over the past four years at least five military prosecutors have resigned from their jobs or from their cases at Guantánamo because they felt their integrity would otherwise be compromised, citing tainted evidence obtained under torture and political interference. As De Beauvoir's quote indicates, there is nothing uniquely American about any of this. The US programme was modelled on Soviet techniques and has been made possible by the cooperation of other nations, including Britain, that have colluded with rendition. According to the New York Times, the former director of the CIA's clandestine service described Poland, where a large amount of the torturing took place, as "the 51st state".

Put the British in Ireland or the Belgians in the Congo and you get the same result. Gordon Brown's bid for 42-day detention without charge fits the mould perfectly. Occupations abroad ineluctably dovetail with the erosion of liberties at home. The only difference seems to be that, on paper at least, the US has set itself higher standards - a fact that exhausts its one truly renewable resource: innocence. "How on earth did we get to the point where a US government lawyer would say that ... torture is subject to perception?" asked Carl Levin, the chairman of the Senate armed services committee, last week. How indeed?

As one inmate warned a US diplomat after he was finally released from prison following torture and a show trial. "Every individual American should realise that what happened to me could happen to anybody." His name? Robert Vogeler.